Optical reflections are undesirable in many fields, such photovoltaics (e.g., solar cells), lighting (e.g., light emitting diodes), displays (e.g., computer displays and televisions), windows (e.g., windshields), sensors, detectors, gun sights, binoculars, spectacles and sunglasses. For example, a substantial portion (e.g., 30 percent or more) of the sunlight applied to a typical silicon solar cell may be reflected at the surface of the solar cell, thereby significantly reducing the amount of light absorbed by the solar cell and, hence, the amount of electrical energy that may be generated by the solar cell.
Optical reflections occur at the interface between two materials having substantially different indices of refraction. For example, in a silicon solar cell, the optical reflection occurs at the air-to-solar cell interface because air has an index of refraction that is substantially less than the index of refraction of silicon.
Various anti-reflection coatings have been developed in an attempt to reduce optical reflections. More recently, anti-reflection nanostructures have been developed to reduce optical reflections. Both traditional index-matched coatings and modern anti-reflection nanostructures reduce optical reflections because the apparent index of refraction of the anti-reflection layer is less than, and transitions to, the index of refraction of the underlying substrate. Nonetheless, additional improvement in optical reflection reduction is desired.
Accordingly, those skilled in the art continue with research and development efforts in the field of anti-reflection.